Abstract
The phylogeny of the six species of the Balanus amphitrite complex found in Japan was analyzed based on nucleotide sequences of the mitochondrial COI (cytochrome oxidase subunit I) gene and the morphology of the barnacles. The six species are B. amphitrite Darwin, B. eburneus Gould, B. improvisus Darwin, B. albicostatus Pilsbry, B. kondakovi Tarasov and Zevina, and B. reticulatus Utinomi. Judging from the high bootstrap values in the sequence-based phylogeny, these six species appear to comprise a monophyletic group divided into two clusters of three species each: B. amphitrite, B. eburneus, and B. improvisus; and B. albicostatus, B. kondakovi, and B. reticulatus. The cladogram based on morphology is congruent with the sequence-based one; the first species cluster is characterized by a multidenticulate labrum, the second by a simple labrum.
